1. Field of the Invention
The present invention relates to a closed loop type fuel cell system.
2. Description of the Related Art
Fuel cells are systems that generate electricity, using reaction between fuel (LNG, LGP, hydrogen, and methanol) and oxygen, and produces water and heat as byproducts, and which are electric generation devices having high electric generation efficiency without factors polluting the environment.
The fuel cells are classified into a polymer electrolyte membrane fuel cell (PEMFC), a direct methanol fuel cell (DMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), and the like, in accordance with the types of electrolytes.
The PEMFC, PAFC, and DMFC in the fuel cells has low operation temperatures of 80 to 120° C., 190 to 200° C., and 25 to 90° C., respectively, and useful for the power sources of transport, such as vehicles, home, and portable devices.
Therefore, researches of reducing the size, weight, and cost of the entire fuel cell systems have been conducted to advance and increase common use of the fuel cells.
However, a large amount of byproducts are produced in an operation environment at a high-current region in the fuel cells and supply of gas to the catalytic layer and dispersion of protons to the polymer film are prevented by droplets of excessive water, such that the performance of the fuel cells is deteriorated.
It is more serious that it is difficult to implement normal operation by reduction of performance of some cells due to non-uniform distribution of water in unit cells disposed in the fuel cells.
As described above, the excessive water produced in the fuel cells, that is, flooding is an important factor that makes normal operation of the fuel cells difficult, in addition to reducing reaction efficiency, it is necessary to discharge the excessive water outside the fuel cells.
Accordingly, “a method and device for performing internal purge infuel cell system” is disclosed in Korean Patent No. 0509818.
The related art is briefly described. Voltages of a plurality of cells are sensed, water and gas mixture in a stack is purged outside the stack by using a pressure difference, by controlling a purge valve and a recirculation pump when flooding occurs, and the gas separated from the water can be re-supplied to the stack.
However, the related art described above has the following problems.
That is, since the degree of purity of the fuel supplied to the fuel cell cannot be 100%, impurities collect in the fuel cell even if the gas separated from the water is re-supplied to the fuel cell, such that electric generation efficiency is reduced.
Further, when carbon of the separator and electrodes in the fuel cell and impurities, such as metal ions and particles of the peripheral components of the fuel cell collect, durability of the fuel cell is gradually influenced and current leaks in the cell, which reduces the life span or damages the fuel cell causes a large amount of repairing charges, and this is not preferable.
Further, even if the water produced in the fuel cell is removed by recirculating the gas in the fuel cell by using the related art, the impurities flow back into the fuel cell by the gas supplied to the fuel cell, because it is a closed circuit, such that performance and durability of the fuel cell are reduced.